A prior art nozzle head of the kind as herein referred is described in U.K. Pat. No. 2,026,359. The hand piece comprises a member in the form of a sleeve fixed to a first connector member having two axially parallel bores to which two flexible supply tubes surrounded by said sleeve are connected for supplying the nozzle head with an abrasive powder material in mixture with air under pressure and with water, resprectively, as delivered from a dental prophylactic apparatus. The first connector member in turn is connected with a second connector member by means of two slightly angled ridgid tubes of which the one tube in turn is connected with a central bore of this second connector member whereas the other tube in turn is connected with a coaxially arranged second bore in such a manner that the common axis of these two bores into which an inner tube and an outer tube, respectively, are fixedly inserted intersects the axes of the two supply tubes each at a right angle in such mutually apart positions that the supply tube for the abrasive powder material in mixture with air under pressure is connected through said central bore to said inner tube upstream to a circular gap which is provided between said inner tube and said outer tube and which is connected through a transverse bore to the supply tube for water. The inner tube which actually projects over said second connector member ends in a first orifice of the nozzle head as does also the outer tube that accordingly ends in a second orifice at an axially projecting position in respect to said first orifice to thereby obtain an ejection of water from said second orifice that surrounds the central ejection of air under pressure in mixture with the abrasive powder material as provided by said first orifice of the nozzle head for their common application to the surface of a tooth which is to be cleaned by the dentist through any suitable manipulation of the hand piece.
However, the employment of such known nozzle heads still has some considerable disadvantages among which first their relative complex structure resulting in respectively high manufacturing and assembling costs may be stated. Secondly, with such known nozzle heads there generally exists the danger of a clogging of the inner tube of the second connector member mainly at the position where its interconnected bore intersects the supply tube for the abrasive powder material in mixture with the air stream due to the fact that the vacuum zone which is created by the water stream at the orifice of the outer tube causes a suction that draws water droplets in the form of a very fine mist into the inner tube so that the inner wall of the same becomes wet. There further exists with such known nozzle heads in general the system bound disadvantage that with the removal of stains and of plaque and light tartar as therewith practiced a more or less eroded tooth surface with a characteristic dull appearance due to the abrasive action of the abrasive laden air jet may be left so that with the usually followed polishing of the cleaned tooth surface a sometimes considerable loss of the tooth enamal surface could be the rule.